Phrasal verbs are combinations of verbs with an adjective or a preposition that function similar to an idiom, have a specific meaning to them and can be used in sentences. The meaning of the phrasal verbs given in the options are:
Option A) turn off: make someone feel bored or uninterested
Option B) turn up: arrive unexpectedly at someone's place
Option C) turn down: refuse or reject someone's offer OR reduce or lower the sound levels
Option D) turn on: to make someone interested in something
The sentence mentions about it being 'loud'. Therefore, the most likely phrasal verb to fill in the blank is option C) turn down. This completes the sentence meaningfully and is in context of the given sentence. The other options are out of context for the given sentence and so are incorrect answers.